//Given a binary tree, check whether it is a mirror of itself (ie, symmetric aro
//und its center). 
//
// For example, this binary tree [1,2,2,3,4,4,3] is symmetric: 
//
// 
//    1
//   / \
//  2   2
// / \ / \
//3  4 4  3
// 
//
// 
//
// But the following [1,2,2,null,3,null,3] is not: 
//
// 
//    1
//   / \
//  2   2
//   \   \
//   3    3
// 
//
// 
//
// Follow up: Solve it both recursively and iteratively. 
// Related Topics 树 深度优先搜索 广度优先搜索


//leetcode submit region begin(Prohibit modification and deletion)
/**
 * Example:
 * var ti = TreeNode(5)
 * var v = ti.`val`
 * Definition for a binary tree node.
 * class TreeNode(var `val`: Int) {
 *     var left: TreeNode? = null
 *     var right: TreeNode? = null
 * }
 */
class Solution {
    fun isSymmetric(root: TreeNode?): Boolean {

    }
}
//leetcode submit region end(Prohibit modification and deletion)
